Stabilization of polymeric material against ultra-violet radiation degradation



United States Patent 3,533,991 STABILIZATION OF POLYMERIC MATERIAL AGAINST ULTRA-VIOLET RADIATION DEG- RADATION Kshatra Pati Singh, Montreal, Quebec, Canada, assignor to Union Carbide Canada Limited, Toronto, Ontario, Canada, a company of Canada No Drawing. Continuation-impart of application Ser. No. 711,863, Mar. 11, 1968. This application Oct. 13, 1969, Ser. No. 866,021

Int. Cl. C08f 45/58, 45/60 US. Cl. zen-45.8 4 Claims ABSTRACT OF THE DISCLOSURE Certain novel polyolefin compositions are prepared which have improved resistance to degradation due to ultra-violet radiation. The compositions consist of a polyolefin such as polyethylene having incorporated therein certain benzoyl pyridine derivatives together with an antioxidant such as di-t-butyl p-cresol.

This application is a continuation-in-part of application Ser. No. 711,863, filed Mar. 11, 1968, and now abandoned.

This invention relates to the stabilization of lower polyolefins against ultra violet degradation. More particularly it relates to lower polyolefins which are stabilized against ultra violet degradation by having incorporated therein a stabilizing amount of certain benzoyl pyridine derivatives and an antioxidant.

The problem of degradation of certain lower olefins such as polyethylene when exposed to ultraviolet radiation is well known. This problem is most acute in high density grades of polyolefin. For example, for reasons of economy, blow moulded polyethylene bottles must be capable of withstanding the impact which results during normal use over prolonged periods. Polyethylene bottles frequently become embrittled and discoloured on prolonged exposure to ultra violet radiation from sunlight. This shortens the life span of such bottles and, particularly in the case of milk bottles, the discolouring elfect is detrimental to customer appeal.

In the increased use of moulded polyethylene for structural purposes the problem of ultra-violet degradation is even more acute. In such uses as beverage containers, stadium seats and patio furniture the polyethylene must be capable of being exposed to ultra-violet radiation over a period of years. It is therefore extremely important that steps be taken to stabilize such structures from degradation over a relatively long life span.

It is therefore an object of the present invention to provide a polyolefin composition having improved stability against ultra violet degradation.

It is another object of the present invention to provide a method of stabilizing certain polyolefins by incorporation into said polyolefin a stabilizing amount of certain benzoyl pyridine derivatives together with an antioxidant.

It has been found that elfective stabilization of lower polyolefins agains degradation due to exposure to ultra violet radiation can be obtained by incorporating certain benzoyl pyridine derivatives into the polyolefin together with certain antioxidants. The stabilizers which are useful in the present invention are those benzoyl pyridine derivatives which show a maximum in their ultra violet adsorption spectra within the range of from 300 to 360 Inn.

The present invention therefore provides a composition having improved resistance to degradation on exposure to ultra violet radiation which comprises a polyolefin of from 2 to 4 carbon atoms and having incorporated therein Patented Oct. 13., 1970 "ice in which R is a radical selected from the group consisting of hydrogen, hydroxyl and an alkoxy group having from 1 to 4 carbon atoms.

The polyolefins which may be stabilized by the pyridine derivatives disclosed in this application are polymerized olefins of from 2 to 4 carbon atoms such as polyethylene and polypropylene. In view of the susceptibility of high density polyethylene to ultra violet degradation the stabilizers of the present application are particularly suited in polyethylene having a density of from 0.941 gram/cc. to 0.965 gram/cc.

Although suitable stabilized polyolefin compositions can be obtained by adding a stabilizing amount of a benzoyl pyridine of the formula mentioned above, preferred stabilizers are selected from compounds of the following formula:

in which R is radical selected from the group consisting of hydrogen, hydroxyl and methoxy.

The benzoyl pyridine derivatives which are particularly suitable as ultra violet stabilizers in polyethylene of a density of from 0.941 to 0.964 gram/cc. is one selected from the group consisting of 2-benzoyl pyridine and 2- (2'-hydroxy) benzoyl pyridine.

Certain antioxidants are also required to be used in conjunction with the benzoyl pyridine derivatives to give the desired stabilizing effect to lower olefins against degradation due to ultra violet radiation. The antioxidants found particularly suitable for this purpose are di-t-butyl p-cresol, di-lauryl thio-dipropionate and 4,4-thiobis (6-tbutyl 3-methyl) phenol. In order to be effective a concentration of one of such antioxidants in a range of from 0.05% to 0.2% by weight of total composition.

EXAMPLE 1 30 gm. of alpha-picolinic acid is treated with 100 ml. of thionyl chloride over 10-20 minutes period and the mixture heated on steam bath for 30 minutes; then the excess of thionyl chloride is distilled off. After most of the thionyl chloride has been distilled, 100 ml. of anhydrous benzene is added and the benzene is distilled at reduced pressure. An additional 100 ml. of anhydrous benzene is added and 60 gm. of anhydrous aluminum chloride is added over a period of 30 minutes which maintaining a low temperature with an ice-salt bath. The mixture is then heated under reflux for 23 hours.

The dark mixture so obtained is poured over 100 gm. of ice and 50 ml. of concentrated hydrochloric acid. The organic layer is separated and discarded. The acid solution is extracted with three 50 ml. portions of ether, which are discarded; then it is treated with 50% aqueous sodium hydrozide until the aluminum hydroxide which first forms redissolves. After cooling, the organic material is extracted with three 50 ml. portions of chloroform. The combined chloroform extracts are washed with water, dried and distilled under vacuum. The yield of 2-benzoyl pyridine, B.P. l35145/5 mm., is 29 gm. (-90%).

3 The structure of the compound was confirmed by elemental and infra-red analysis.

The effectiveness of the product as a stabilizer against degradation by ultra violet radiation of a high density grade of polyethylene (density: 0.957 and melt index:

4 EXAMPLE 5 A test piece was prepared containing 0.05 percent by weight of Z-benzoyl pyridine and 0.1 percent by weight of 4,4-thiobis (6-t-butyl 3-methyl) phenol based on the weight of polyethylene. Again the amount of em- 0.35) was determined by incorporating the productdnt 5 brittlement after 65 hours of ultra-violet exposure was the Polyethylene on a two-T011 min and forming test Pleces slight and the amount of discoloration was within acceptby compression molding, the test pieces having the followable limits for most commercial uses ing dimensions: 3 x 1" x 0.04". Except for the first test the test pieces also contained an antioxidant. 1O EXAMPLE 6 The test pieces were exposed to the l gh f om a A test piece was prepared containing 0.15 percent by watt ultra violet lamp for varying periods of time and weight f 2-benzoy1 pyridine, 0.1 percent by weight of the resulting discoloration and degree of embrittlement di t-buty1 1 d Q1 percent b i ht f di 1 1 were noted after 18 and 65 hOurS- The discolorati n WflS thio-dipropionate. After 65 hours of ultra violet exposure determinfid Visually and given a numerical rating in the 1 it exhibited very little embrittlement and less discolorarange of 0 to 6, where 0 indicated no discoloration and tion than th te t i c of Example 5, 6 indicates extensive discoloration.

The degree of embrittlement was rated by the ease of EXAMPLE 7 cracking on repeated flexing of the specimen. As in the A test piece was prepared containing 0.15 percent by case of discoloration, the degree of embrittlement was 20 Weight of 2-benzoyl pyridine and 0.05 percent by weight rated numerically from 0 to 6 with 0 indicating no emof 4,4-thiobis (6-t-butyl 3-methyl) phenol. The test piece brittlement and 6 indicating extensive embrittlement. showed very little embrittlement after 65 hours of ultra The first test piece contained Z-benzoyl pyridine in an violet exposure. While discoloration was apparent it was amount of approximately 0.05 percent by weight based Within usually acceptable commercial limits. on the weight of polyethylene. No antioxidant was used EXAMPLE 8 in this test sample. The amount of discoloration was not significant and did not increase much after 65 hours. The A test Piece was P P containing 025 Parcent by degree of embrittlement however was given a rating of Weight of y P y salicylate instead of z-benzoyl 5 ft 5 hours, pyridine, 0.1 percent by weight of d-t-butyl p-cresol and EXAMPLE 2 0.1 percent by weight of di-lauryl thio-dipropionate. Considerable discoloration was exhibited after 18 hours of A test piece was prepared as described in Example 1 ultra violet exposure which increased to severe discoloracontaining no benzoyl pyridine but containing 0.1 percent tion after 65 hours. The test piece also exhibited considerby weight of di-t-butyl p-cresol and 0.1 percent by weight able embrittlement. of di-lauryl thio-dipropionate. While the amount of dis- The results of the above test are tabulated in the followcoloration after 18 hours was not noticeable and was only ing table:

TABLE I Exposure 18 hours 65 hours Antioxidant in Stabilizer in percent by percent by Discol- Embrit- Discol- Embritweight weight; oration tlement oration tlement Test No.:

a do TBMP,0.2 0 1 1 5 4 2 benzoyl pyridine, 0-05 g% 5: 1:} 3 0 3 2 5 do TBMP, 0.1 3 1 4 2 6 2 benzoyl pyridine, 0.15. 3 1 3 2 7 d0 TBMP, 0.05-

4 2 4 2 8 38,025 gttgt itizzzzl 5 0 6 5 D B P O is di-t-butyl p-cresol.

o'rE: TBS is 4-t-butyl phenyl salicylate.

DLTDP is di-lauryl thio-dipropionate. TBMP is 4,4-thiobis (6-t-butyl 3-methyl) phenol.

In this test the polyethylene piece contained 0.05 percent by weight of 2'benzoyl pyridine, 0.05 percent by weight of di-t-butyl cresol and 0.05 percent by Weight of di-lauryl thio-dipropionate based on the weight of the polyethylene. While an amount of discoloration appeared after 18 hours this did not increase after 65 hours and the test piece showed very slight embrittlement.

From the results of Tests Nos. 1 to 7, it may be seen that although after 18 hours exposure there was no significant difference between the embrittlement of stabilized and unstabilized sample, the test pieces containing only 2-benzoyl pyridine or anti-oxidants showed significant embrittlement after 65 hours exposure Whereas, for the test piece containing both Z-benzoyl pyridine and antioxidant there was less embrittlement after 65 hours.

The results of Test No. 8 are included in Table I to to illustrate how much more effective is the Z-benzoyl pyridine in retarding degradation due to ultra violet radiation than is another well known ultra violet stabilizer.

I claim:

1. A composition having improved resistance to degradation on exposure to ultra violet radiation which comprises a polymer of an olefin having from 2 t0 4 carbon atoms and having incorporated therein a stabilizing amount of 2-benzoy1 pyridine together With an effective amount of an antioxidant selected from the group consisting of di-t-butyl p cresol, di-lauryl thio-dipropionate and 4,4'-thiobis (6-t-buty1 3-methyl) phenol.

2. A composition as claimed in claim 1 wherein from 0.01 percent by weight to 5 percent by weight of 2benzoyl pyridine is incorporated into the polymer.

3. A composition as claimed in claim 2 wherein the polymer is polyethylene having a density of from 0.941 to 0.964 grams/cc.

4. A composition as claimed in claim 3 wherein from 0.05 percent by weight to 1 percent by weight of 2-benzoyl pyridine is incorporated into the polyethylene.

References Cited UNITED STATES PATENTS DONALD E. CZAJR, Primary Examiner 0 R. A. WHITE, Assistant Examiner US. Cl. X.R. 

